1. Technical Field
This invention relates generally to a reciprocating engine fueled on any fuel that can be ignited by ignition spark or other high energy ignition system suitable for use in heavy-duty vehicle applications, and more particularly to such an engine having high efficiency while producing low emissions. For purposes of this invention, flame propagation engines are ones in which a mixture of fuel and air is created and ignited in-cylinder by suitable means. The resulting flame travels through the fuel-air mixture. Conventional spark ignition engines are examples of this type of engine. This is opposed to a diffusion burn type engine, like a conventional Diesel engine, in which most of the fuel burns in a diffusion manner.
2. Background Art
The U.S. Environmental Protection Agency (EPA) has set very stringent emissions standards for heavy-duty vehicles that would reduce smog-causing emissions from trucks, buses and motor homes. The emissions standards set forth for model year 2007 include two components, emissions standards and Diesel fuel regulation. The first component of the regulation introduces new, very stringent emission standards, as follows:                Particulate matter (PM)—0.01 g/bhp-hr        Nitrogen oxide (NOx)—0.20 g/bhp-hr        Non-methane hydrocarbons (NMHC)—0.14 g/bhp-hr.        
The particulate matter emissions standard will take full effect in the 2007 heavy-duty engine model year. The NOx and NMHC standards will be phased in for Diesel engines between 2007 and 2010. The phase-in would be on a percent-of-sales basis: 50% in 2007–2009, and 100% in 2010. Gasoline engines are subject to the same standards based on a phase-in requiring 50% compliance in 2008 and 100% compliance in 2009. The Diesel fuel regulation limits the sulfur content in on-highway Diesel fuel to 15 ppm (wt.), down from the previous 500 ppm. Refiners will be required to start producing the 15 ppm sulfur fuel beginning Jun. 1, 2006. Ultra-low sulfur Diesel fuel has been mandated as a “technology enabler” to pave the way for advanced, sulfur-intolerant exhaust emission control technologies, such as catalytic Diesel particulate filters, lean NOx adsorbers, and NOx catalysts, all of which will be necessary to meet the 2007 emissions standards. Moreover, it is anticipated that significant engine modifications will be required, such as a high pressure common rail, massive cooled exhaust gas recirculation, low pressure loop exhaust gas recirculation after a particulate matter trap, high boost provided by a supercharger or turbocharger, NOx sensors, model-based control schemes, and on-board diagnostic (OBD) systems. PM control will require catalyzed particulate matter traps, and NOx control will require NOx adsorbers. Therefore, it is essential that low sulfur fuel be available to meet the performance requirements of the catalyzed PM traps and NOx adsorbers.
Diesel engines have traditionally been considered as the most efficient reciprocating engine. However, NOx emissions are typically one hundred times those produced by spark ignition engines and PM emissions are one thousand times those produced by spark ignition engines. Moreover, Diesel engines cost twenty to forty percent more than a comparable horsepower flame propagation engine. When comparing the viability of a flame propagation engine to replace a Diesel engine in heavy-duty applications, the comparison must be made at the same emissions levels. The Diesel engine needs PM traps and lean NOx adsorbers. Thus, Diesel engine costs at the same emissions level are a factor of 2–3 more. Morever Diesel efficiency approaches that of flame propagation engines at the future mandated emissions levels.
For heavy-duty Diesel vehicles, the EPA categorizes Classes 2B thru 5 (8,501 to 19,500 gross vehicle weight rating (GVWR)) as light heavy-duty, Classes 6 and 7 (19,501 to 33,000 GVWR) are categorized as medium heavy-duty, and Class 8 (33,000 GVWR and above) as heavy heavy-duty.
The present invention is directed to overcoming the inherent problems, i.e., the difficulty and expense associated with achieving future emissions reductions in Diesel engines. It is desirable to have an engine for heavy-duty vehicular applications that takes advantage of the lower cost and lower emissions inherently provided by flame propagation engines and has an operating efficiency (BSFC) comparable to that of Diesel engines. Such an engine would readily replace Diesel engines in all classes of heavy-duty vehicular applications, thereby greatly reducing pollution attributable to vehicles falling within those classes.